<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1988-2017 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software" and "Free Software Needs
Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
and with the Back-Cover Texts as in (a) below.

(a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom." -->
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
<head>
<title>Debugging with GDB: Events In Python</title>

<meta name="description" content="Debugging with GDB: Events In Python">
<meta name="keywords" content="Debugging with GDB: Events In Python">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="index.html#Top" rel="start" title="Top">
<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Python-API.html#Python-API" rel="up" title="Python API">
<link href="Threads-In-Python.html#Threads-In-Python" rel="next" title="Threads In Python">
<link href="Inferiors-In-Python.html#Inferiors-In-Python" rel="prev" title="Inferiors In Python">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.indentedblock {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
div.smalllisp {margin-left: 3.2em}
kbd {font-style:oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nocodebreak {white-space:nowrap}
span.nolinebreak {white-space:nowrap}
span.roman {font-family:serif; font-weight:normal}
span.sansserif {font-family:sans-serif; font-weight:normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<a name="Events-In-Python"></a>
<div class="header">
<p>
Next: <a href="Threads-In-Python.html#Threads-In-Python" accesskey="n" rel="next">Threads In Python</a>, Previous: <a href="Inferiors-In-Python.html#Inferiors-In-Python" accesskey="p" rel="prev">Inferiors In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Events-In-Python-1"></a>
<h4 class="subsubsection">23.2.2.17 Events In Python</h4>
<a name="index-inferior-events-in-Python"></a>

<p><small>GDB</small> provides a general event facility so that Python code can be
notified of various state changes, particularly changes that occur in
the inferior.
</p>
<p>An <em>event</em> is just an object that describes some state change.  The
type of the object and its attributes will vary depending on the details
of the change.  All the existing events are described below.
</p>
<p>In order to be notified of an event, you must register an event handler
with an <em>event registry</em>.  An event registry is an object in the
<code>gdb.events</code> module which dispatches particular events.  A registry
provides methods to register and unregister event handlers:
</p>
<dl>
<dt><a name="index-EventRegistry_002econnect"></a>Function: <strong>EventRegistry.connect</strong> <em>(object)</em></dt>
<dd><p>Add the given callable <var>object</var> to the registry.  This object will be
called when an event corresponding to this registry occurs.
</p></dd></dl>

<dl>
<dt><a name="index-EventRegistry_002edisconnect"></a>Function: <strong>EventRegistry.disconnect</strong> <em>(object)</em></dt>
<dd><p>Remove the given <var>object</var> from the registry.  Once removed, the object
will no longer receive notifications of events.
</p></dd></dl>

<p>Here is an example:
</p>
<div class="smallexample">
<pre class="smallexample">def exit_handler (event):
    print &quot;event type: exit&quot;
    print &quot;exit code: %d&quot; % (event.exit_code)

gdb.events.exited.connect (exit_handler)
</pre></div>

<p>In the above example we connect our handler <code>exit_handler</code> to the
registry <code>events.exited</code>.  Once connected, <code>exit_handler</code> gets
called when the inferior exits.  The argument <em>event</em> in this example is
of type <code>gdb.ExitedEvent</code>.  As you can see in the example the
<code>ExitedEvent</code> object has an attribute which indicates the exit code of
the inferior.
</p>
<p>The following is a listing of the event registries that are available and
details of the events they emit:
</p>
<dl compact="compact">
<dt><code>events.cont</code></dt>
<dd><p>Emits <code>gdb.ThreadEvent</code>.
</p>
<p>Some events can be thread specific when <small>GDB</small> is running in non-stop
mode.  When represented in Python, these events all extend
<code>gdb.ThreadEvent</code>.  Note, this event is not emitted directly; instead,
events which are emitted by this or other modules might extend this event.
Examples of these events are <code>gdb.BreakpointEvent</code> and
<code>gdb.ContinueEvent</code>.
</p>
<dl>
<dt><a name="index-ThreadEvent_002einferior_005fthread"></a>Variable: <strong>ThreadEvent.inferior_thread</strong></dt>
<dd><p>In non-stop mode this attribute will be set to the specific thread which was
involved in the emitted event. Otherwise, it will be set to <code>None</code>.
</p></dd></dl>

<p>Emits <code>gdb.ContinueEvent</code> which extends <code>gdb.ThreadEvent</code>.
</p>
<p>This event indicates that the inferior has been continued after a stop. For
inherited attribute refer to <code>gdb.ThreadEvent</code> above.
</p>
</dd>
<dt><code>events.exited</code></dt>
<dd><p>Emits <code>events.ExitedEvent</code> which indicates that the inferior has exited.
<code>events.ExitedEvent</code> has two attributes:
</p><dl>
<dt><a name="index-ExitedEvent_002eexit_005fcode"></a>Variable: <strong>ExitedEvent.exit_code</strong></dt>
<dd><p>An integer representing the exit code, if available, which the inferior 
has returned.  (The exit code could be unavailable if, for example,
<small>GDB</small> detaches from the inferior.) If the exit code is unavailable,
the attribute does not exist.
</p></dd></dl>
<dl>
<dt><a name="index-ExitedEvent"></a>Variable: <strong>ExitedEvent</strong> <em>inferior</em></dt>
<dd><p>A reference to the inferior which triggered the <code>exited</code> event.
</p></dd></dl>

</dd>
<dt><code>events.stop</code></dt>
<dd><p>Emits <code>gdb.StopEvent</code> which extends <code>gdb.ThreadEvent</code>.
</p>
<p>Indicates that the inferior has stopped.  All events emitted by this registry
extend StopEvent.  As a child of <code>gdb.ThreadEvent</code>, <code>gdb.StopEvent</code>
will indicate the stopped thread when <small>GDB</small> is running in non-stop
mode.  Refer to <code>gdb.ThreadEvent</code> above for more details.
</p>
<p>Emits <code>gdb.SignalEvent</code> which extends <code>gdb.StopEvent</code>.
</p>
<p>This event indicates that the inferior or one of its threads has received as
signal.  <code>gdb.SignalEvent</code> has the following attributes:
</p>
<dl>
<dt><a name="index-SignalEvent_002estop_005fsignal"></a>Variable: <strong>SignalEvent.stop_signal</strong></dt>
<dd><p>A string representing the signal received by the inferior.  A list of possible
signal values can be obtained by running the command <code>info signals</code> in
the <small>GDB</small> command prompt.
</p></dd></dl>

<p>Also emits  <code>gdb.BreakpointEvent</code> which extends <code>gdb.StopEvent</code>.
</p>
<p><code>gdb.BreakpointEvent</code> event indicates that one or more breakpoints have
been hit, and has the following attributes:
</p>
<dl>
<dt><a name="index-BreakpointEvent_002ebreakpoints"></a>Variable: <strong>BreakpointEvent.breakpoints</strong></dt>
<dd><p>A sequence containing references to all the breakpoints (type 
<code>gdb.Breakpoint</code>) that were hit.
See <a href="Breakpoints-In-Python.html#Breakpoints-In-Python">Breakpoints In Python</a>, for details of the <code>gdb.Breakpoint</code> object.
</p></dd></dl>
<dl>
<dt><a name="index-BreakpointEvent_002ebreakpoint"></a>Variable: <strong>BreakpointEvent.breakpoint</strong></dt>
<dd><p>A reference to the first breakpoint that was hit.
This function is maintained for backward compatibility and is now deprecated 
in favor of the <code>gdb.BreakpointEvent.breakpoints</code> attribute.
</p></dd></dl>

</dd>
<dt><code>events.new_objfile</code></dt>
<dd><p>Emits <code>gdb.NewObjFileEvent</code> which indicates that a new object file has
been loaded by <small>GDB</small>.  <code>gdb.NewObjFileEvent</code> has one attribute:
</p>
<dl>
<dt><a name="index-NewObjFileEvent_002enew_005fobjfile"></a>Variable: <strong>NewObjFileEvent.new_objfile</strong></dt>
<dd><p>A reference to the object file (<code>gdb.Objfile</code>) which has been loaded.
See <a href="Objfiles-In-Python.html#Objfiles-In-Python">Objfiles In Python</a>, for details of the <code>gdb.Objfile</code> object.
</p></dd></dl>

</dd>
<dt><code>events.clear_objfiles</code></dt>
<dd><p>Emits <code>gdb.ClearObjFilesEvent</code> which indicates that the list of object
files for a program space has been reset.
<code>gdb.ClearObjFilesEvent</code> has one attribute:
</p>
<dl>
<dt><a name="index-ClearObjFilesEvent_002eprogspace"></a>Variable: <strong>ClearObjFilesEvent.progspace</strong></dt>
<dd><p>A reference to the program space (<code>gdb.Progspace</code>) whose objfile list has
been cleared.  See <a href="Progspaces-In-Python.html#Progspaces-In-Python">Progspaces In Python</a>.
</p></dd></dl>

</dd>
<dt><code>events.inferior_call_pre</code></dt>
<dd><p>Emits <code>gdb.InferiorCallPreEvent</code> which indicates that a function in
the inferior is about to be called.
</p>
<dl>
<dt><a name="index-InferiorCallPreEvent_002eptid"></a>Variable: <strong>InferiorCallPreEvent.ptid</strong></dt>
<dd><p>The thread in which the call will be run.
</p></dd></dl>

<dl>
<dt><a name="index-InferiorCallPreEvent_002eaddress"></a>Variable: <strong>InferiorCallPreEvent.address</strong></dt>
<dd><p>The location of the function to be called.
</p></dd></dl>

</dd>
<dt><code>events.inferior_call_post</code></dt>
<dd><p>Emits <code>gdb.InferiorCallPostEvent</code> which indicates that a function in
the inferior has returned.
</p>
<dl>
<dt><a name="index-InferiorCallPostEvent_002eptid"></a>Variable: <strong>InferiorCallPostEvent.ptid</strong></dt>
<dd><p>The thread in which the call was run.
</p></dd></dl>

<dl>
<dt><a name="index-InferiorCallPostEvent_002eaddress"></a>Variable: <strong>InferiorCallPostEvent.address</strong></dt>
<dd><p>The location of the function that was called.
</p></dd></dl>

</dd>
<dt><code>events.memory_changed</code></dt>
<dd><p>Emits <code>gdb.MemoryChangedEvent</code> which indicates that the memory of the
inferior has been modified by the <small>GDB</small> user, for instance via a
command like <code>set&nbsp;*addr&nbsp;=&nbsp;value</code><!-- /@w -->.  The event has the following
attributes:
</p>
<dl>
<dt><a name="index-MemoryChangedEvent_002eaddress"></a>Variable: <strong>MemoryChangedEvent.address</strong></dt>
<dd><p>The start address of the changed region.
</p></dd></dl>

<dl>
<dt><a name="index-MemoryChangedEvent_002elength"></a>Variable: <strong>MemoryChangedEvent.length</strong></dt>
<dd><p>Length in bytes of the changed region.
</p></dd></dl>

</dd>
<dt><code>events.register_changed</code></dt>
<dd><p>Emits <code>gdb.RegisterChangedEvent</code> which indicates that a register in the
inferior has been modified by the <small>GDB</small> user.
</p>
<dl>
<dt><a name="index-RegisterChangedEvent_002eframe"></a>Variable: <strong>RegisterChangedEvent.frame</strong></dt>
<dd><p>A gdb.Frame object representing the frame in which the register was modified.
</p></dd></dl>
<dl>
<dt><a name="index-RegisterChangedEvent_002eregnum"></a>Variable: <strong>RegisterChangedEvent.regnum</strong></dt>
<dd><p>Denotes which register was modified.
</p></dd></dl>

</dd>
<dt><code>events.breakpoint_created</code></dt>
<dd><p>This is emitted when a new breakpoint has been created.  The argument
that is passed is the new <code>gdb.Breakpoint</code> object.
</p>
</dd>
<dt><code>events.breakpoint_modified</code></dt>
<dd><p>This is emitted when a breakpoint has been modified in some way.  The
argument that is passed is the new <code>gdb.Breakpoint</code> object.
</p>
</dd>
<dt><code>events.breakpoint_deleted</code></dt>
<dd><p>This is emitted when a breakpoint has been deleted.  The argument that
is passed is the <code>gdb.Breakpoint</code> object.  When this event is
emitted, the <code>gdb.Breakpoint</code> object will already be in its
invalid state; that is, the <code>is_valid</code> method will return
<code>False</code>.
</p>
</dd>
</dl>

<hr>
<div class="header">
<p>
Next: <a href="Threads-In-Python.html#Threads-In-Python" accesskey="n" rel="next">Threads In Python</a>, Previous: <a href="Inferiors-In-Python.html#Inferiors-In-Python" accesskey="p" rel="prev">Inferiors In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>



</body>
</html>
